Engineering the Polymer-MOF Interface in Microporous Composites to Address Complex Mixture Separations

Poor interfacial compatibility remains a pressing challenge in the fabrication of high-performance polymer-MOF composites. In response, introducing compatible chemistries such as a carboxylic acid moiety has emerged as a compelling strategy to increase polymer-MOF interactions. In this work, we leveraged compatible functionalities in UiO-66-NH₂ and a carboxylic acid-functionalized PIM-1 to fabricate mixed-matrix membranes (MMMs) with improved separation performance compared to PIM-1-based MMMs in industrially relevant conditions. Under pure-gas conditions, PIM-COOH-based MMMs retained selectivity with increasing MOF loading and showed increased permeability due to increased diffusion. The composites were further investigated under industrially relevant conditions, including CO₂/N₂, CO₂/CH₄, and H₂S/CO₂/CH₄ mixtures, to elucidate the effects of competitive sorption and plasticization. Incorporation of UiO-66-NH₂ in PIM-COOH and PIM-1 mitigated the effects of CO₂- and H₂S-induced plasticization typically observed in linear polymers. In CO₂-based binary mixed-gas tests, all samples showed similar performance as that in pure-gas tests, with minimal competitive sorption contributions associated with the amine functional groups of the MOF. In ternary mixed-gas tests, improved plasticization resistance and interfacial compatibility resulted in PIM-COOH-based MMMs having the highest H₂S/CH₄ and CO₂/CH₄ selectivity combinations among the films tested in this study. These findings demonstrate that selecting MOFs and polymers with compatible functional groups is a useful strategy in developing high-performing microporous MMMs that require stability under complex and industrially relevant conditions.